Dialkyltin catalyst

Tri-n-butylstannylpropanol was found to be an excellent catalyst, superior to DBTDL, in catalyzing the reaction of aromatic isocyanates with tertiary alcohols. Generally DBTDL and other dialkyltin catalysts show diminished catalysis with secondary and tertiary hydroxyl groups. 

Polyurethane hydrogels are prepared by reaction of a polyisocyanate with polyethyleneglycol. These hydrogels can swell with water and are used in medical applications, such as wound dressings. Although dialkyltin catalysts are claimed in this application, the use of organotin compounds in medical applications with potential contact with blood is questionable, and they are probably not the safest catalysts for this application. 

The activity of a catalyst in a polymer system is not always assured. Dialkyltin catalysts can be deactivated in a formulation, by absorption on a pigment or filler surface, or by ionic impurities. Low pH or strong acids can either inhibit or reduce the reaction rate of DBTDL catalyst systems. In hydroxyl end-capped fluoropolyether polymers, a minimum amount of DBTDL catalyst is required to catalyze the reaction... 

Dialkyltin catalysts (such as dibutyltin dilaurate) have catalytic properties for esterification and alcoholysis similar to Ti and Zr [123]. The Sn-C bond is fairly stable, but the upper acceptable temperature limit is around 220°C. On the other hand, thanks to the added flexibility provided by the organic group and the possibility of oligomerization, it is possible to prepare catalysts that are quite insensitive to deactivation by vestiges of humidity [124], Nowadays these catalysts are often used in alkyd resin production. 

Alkyltin Intermedia.tes, For the most part, organotin stabilizers are produced commercially from the respective alkyl tin chloride intermediates. There are several processes used to manufacture these intermediates. The desired ratio of monoalkyl tin trichloride to dialkyltin dichloride is generally achieved by a redistribution reaction involving a second-step reaction with stannic chloride (tin(IV) chloride). By far, the most easily synthesized alkyltin chloride intermediates are the methyltin chlorides because methyl chloride reacts directiy with tin metal in the presence of a catalyst to form dimethyl tin dichloride cleanly in high yields (21). Coaddition of stannic chloride to the reactor leads directiy to almost any desired mixture of mono- and dimethyl tin chloride intermediates ... 

Dibutyltin diacetate, dilaurate, and di-(2-ethylhexanoate) are used as homogeneous catalysts for room-temperature-vulcanizing (RTV) silicones. The dialkyltin compounds bring about the cross-linking of the oligomeric siloxanes, to produce flexible, silicone rubbers having a host of different uses, such as electrical insulators and dental-impression molds. Recent work has also shown (560) that various dibutyltin dicar-boxylates catalyze both the hydrolysis and gelation of ethyl silicate under neutral conditions. 

Catalysts Catalysts are widely used for PU manufacture. Sometimes a combination of two or three catalysts is required to obtain the desired balance of reaction rates between compounds of differing active hydrogen activity. Metal compounds, especially organotin compounds, are much more efficient catalysts than tertiary amines for the -OH/NCO reaction. In addition to more commonly used dibutyltin(IV) dilaurate, dibutyltin(IV) diacetate, dialkyltin(IV) oxide or salts of divalent fin with a variety of carboxylic acids such as stannous octoate, hexoate and naphthenate etc. are available for this purpose. Combination of tin catalysts with tertiary amines has been reported to lead to a synergistic increase in catalytic activity. 

Peroxo-/i-oxo-bis bisOrimcLhy]si]y])methyl tin (316) is an organotin analog of the FOZ of a symmetrically tetraalkylated olefin (278). It is obtained in low yield by oxidation of the corresponding silylated dialkyltin in the presence of a molybdenum catalyst. The structure was elucidated by XRD analysis and has some characteristic features (a) The 0—0 distance is unusually long (154.3 pm) as compared to that of similar transition metal... 

Dialkyltin dicarboxylates, e g. Bu2Sn(02CCu 1123)2, are useful catalysts for polyurethane foam formation and as cross-linking agents for room-temperature vulcanization. Monobutyltins have been used as catalysts in transesterification and esterification reactions, e.g. in the reaction between phthalic anhydride and 2-ethylhexanol. 

The polycondensation of BHET to PET proceeds in the melt at temperatures of 270-305 °C, under vacuum (< 1 mbar absolute pressure) and in the presence of Lewis acid metal compounds, such as titanium alkoxides, dialkyltin oxide, gallium oxide, germanium oxide, thallium oxide, lanthanide salts, and most commonly, antimony oxide [1,2, 22-26]. Under polymerization reaction conditions, these catalysts are generally converted to their alkoxides with ethylene glycol. Typical of such alkoxides is antimony(III) glycolate, the active catalyst for the majority of the world s PET production [27] (cf. Structure 1). 

Dialkyl aminoethyl acrylic esters are readily prepared by transesterification of the corresponding dialkylaminoethanol (102,103). Catalysts include strong acids and tetraalkyl titanates for higher alkyl esters and titanates, sodium phenoxides, magnesium alkoxides, and dialkyltin oxides, as well as titanium and zirconium chelates, for the preparation of functional esters. Because of loss of catalyst activity during the reaction, incremental or continuous additions may be required to maintain an adequate reaction rate. 

As catalysts, almost exclusively dialkyltin dicarboxylates are used. Since the catalytically active species is the dialkyltin dihydroxide, the original catalyst compound must be first hydrolysed to become effective. It is therefore imperative that a certain level of moisture, i.e. water in vapor form as a cocatalyst, is present in both the rubber system and the ambient atmosphere. 

Derivatives of both two- and four-valent tin have found use as catalysts in urethane foams. In addition to the more commonly used dibutyltin (IV) dilaurate, dibutyltin (IV) diacetate, dialkyltin (IV) oxide or salts of two-valent tin with a variety of carboxylic acids such as stannous octoate, hexoate and naphthenate, there are also available chlorine-containing compounds (dibutyltin dichloride, SnCl2, SnClJ, sulphur-containing compounds (e.g. tributyltin laurylmercaptate), and complexes such as stannous quinolinolate or dibutyltin bis(acetylacetonate). Other catalysts... 

Carboxylates of divalent tin are used almost exclusively for the commercial production of flexible foams. Catalysts containing tetravalent tin, e.g. the dialkyltin dicarboxylates, catalyze oxidation at elevated temperatures. Since temperatures exceeding 140° are often reached during the production of polyurethanes, this can lead to severe degradation unless these catalysts are used in conjunction with small amounts of antioxidants such as substituted phenolics. 

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